1. Field of the Invention
The present invention relates to a photosensor technology, and in particular to a photosensor device with dark current cancellation.
2. Description of the Related Art
In optical application systems, photosensors, such as visible light sensors, infrared sensors, UV sensors, distance sensors and photo signal transmission sensors with optical fibers, can be usually used for converting photo signals into electrical signals. One kind of light sensor made of a photodiode still generates a dark current under no illumination. The dark current is a source of noise, thus it will affect the sensing result. The prior art of U.S. Pat. No. 7,323,672B2 discloses a light sensor structure with dark current compensation. As shown in FIG. 1, two light sensors 31, 32 are connected respectively with a first current-to-pulse converter 33 and a second current-to-pulse converter 34, wherein the light sensors 31, 32 comprise respectively two photodiodes D1, D2. Therefore, two dark currents are generated by the light sensors 31, 32 under no illumination, and the first current-to-pulse converter 33 and the second current-to-pulse converter 34 convert respectively the two dark currents into two pulse signals. Due to the fact that two identical pulse signals are generated from identical photodiodes, the number of the pulse signals are equal. Therefore, the pulse process unit 35 produces zero output voltage, and thereby the noise generated from the dark currents of the two photodiodes can be eliminated. However, in the technology of the prior art, two current to pulse converters 33 and 34 must be utilized in the circuit structure for eliminating the dark current, thus raising its production cost.
In the view of these above mentioned shortcomings in the prior art, the present invention provides a photosensor device with a simple construction and at least an advantage of dark current cancellation, for offering the benefits to the public.